Press felts are used, for example, as fabrics in the wet end of a papermaking machine and are known in a multiplicity of embodiments. Press felt fabrics of this type are an endlessly circulating belt which usually extends over the entire machine width and serves to dewater the paper web in the pressing section of the papermaking machine. In order that the paper web is given a smooth surface free of markings, press felts are as a rule used which have a smooth surface and a uniformly resilient structure. At the same time, a press felt requires a sufficiently high open porosity in order to absorb the water which is to be removed from the wet paper web.
The press felt is pressed against the paper web for mechanically dewatering the paper web by means of a roll which usually has a surface profile for conducting away the water which has been pressed out of the paper web. Here, water contained in the paper web passes into the press felt and, in the ideal case, is transported away completely by the latter in the direction of the roll.
A basic requirement of the fabrics in the pressing section of a papermaking machine comprises dewatering the paper web as much as possible, in order to minimize the energy outlay for the drying section of the paper web which adjoins the pressing section. Rewetting, that is to say part of the water already pressed out of the paper web being sucked back out of the press felt into the paper web, which occurs when the contact pressure of the press felt against the paper web decreases, is to be avoided as far as possible.
The maximum achievable dryness at the outlet of the pressing section of a papermaking machine is limited, however, by adsorption and capillary forces which bind the water within the paper web and on the paper web surface. Theoretically, a dryness of the paper web of from 72 to 76% can be achieved here. In practice, however, only drynesses of at most from 50 to 52% are being achieved at present.
Press felts of the type mentioned in the introduction are known, for example, from DE 102 04 357 B4. The press felt described here has a carrier which has at least one layer of a laid scrim with scrim threads which run parallel to one another and in the plane of the press felt, and is embedded into a fiber matrix. Here, the scrim threads are provided with outwardly projecting fibers and are equipped with channels in order to improve the dewatering properties on their surface, which channels extend between a first end and a second end of the respective scrim threads.